1. Field of the Invention
The present invention relates to voltage controlled oscillators, and more specifically it relates to regulation of the output signal level from voltage controlled oscillators, when used in different applications, further the invention relates to a method for reducing losses in phase locked loops using voltage controlled oscillators.
2. Description of the Prior Art
Voltage controlled oscillators are widely used in generating various frequencies within a specified frequency band.
Typically for such uses the voltage controlled oscillator is incorporated in a phase locked loop.
Such a phase locked loop may incorporate a reference oscillator, a phase detector, a low pass filter, a programmable divider and a voltage, controlled oscillator, all co-operating in the following manner.
The reference oscillator, typically a crystal oscillator, generates a fixed frequency which is supplied to the phase detector on a first line. The phase detector compares the phase of the signal on the first line with the phase of a frequency signal on a second line originating from the voltage controlled oscillator. This frequency signal from the voltage controlled oscillator may be divided down by a programmable divider before the phase comparison in the phase detector takes place. Based on the comparison, the phase detector generates an error signal on a third line, via which it is input to the voltage controlled oscillator. The error signal is in the form of a control voltage signal for the voltage controlled oscillator. Based on the control voltage signal the voltage controlled oscillator generates an output signal on an output line. This signal is at a different frequency from the fixed frequency, depending on the division ratio of the programmable divider.
When using a voltage controlled oscillator in a phase locked loop in modern mobile communications, the operating frequency will typically be in the vicinity of 4 GHz. This signal may then conveniently be divided down with integer factors of 2, 4 and 8, thereby achieving frequencies in the most commonly used frequency bands around 1800 MHz, 1900 MHz, 900 MHz and 450 MHz.
However, operating a phase locked loop at 4 GHz in a mobile phone involves some problems.
At these frequencies the transmission of signals between individual parts of circuit in which the voltage controlled oscillator is incorporated depend very much on the actual design of the circuit in which the voltage controlled oscillator is incorporated. In fact it may in some cases even be a problem transmitting the signal from the voltage controlled oscillator to the programmable divider.
Increasing the output power of the voltage controlled oscillator may in some cases be a way around this problem.
However, it is generally undesired to increase power consumption anywhere in a mobile phone because they are generally battery powered. In fact quite a lot of effort has been put into decreasing the overall power consumption of mobile phones, in order to allow long standby times and long talk times without having to recharge the battery.
Further, programmable dividers for the use at 4 GHz are generally sensitive to too powerful signals.
One reason for this is that their design is inherently unstable, in order to be able to achieve the necessary operating speed for such high frequencies. Thus they are more prone to counting errors resulting in overtones in the output signal when the input signal is too powerful.
Since the voltage controlled oscillator is to be used in different mobile telephone constructions where it has to be ensured both that there is sufficient signal and that the signal is not too powerful, the output power has to be adjusted to the actual application.
Traditionally this has been done by having a voltage controlled oscillator with comparably high output power, and then having an attenuator in the circuit in which the voltage controlled oscillator is incorporated, in order to be able to attenuate the signal if it proves necessary in the particular application. In a phase locked loop the attenuator is found between the output of the voltage controlled oscillator and the input of the programmable divider.
As mentioned earlier, this is in mobile phones in contradiction to the overall object of reducing power consumption.
The present invention provides a voltage controlled oscillator, which may be used in a variety of applications, yet does not suffer from the above drawbacks.
According to the invention a voltage controlled oscillator comprises a voltage controlled oscillator assembly including means for regulating the output power from the at least one voltage controlled oscillator.
The invention reduces losses when using a voltage controlled oscillator in a phase locked loop.
According to the invention a method for reducing losses in a phase locked loop includes a micro-controller, arranged on the same chip as the voltage controlled oscillator, is used for regulating the level of the output signal from the voltage controlled oscillator chip.